Adult female rhesus monkeys will be fed diets containing 25 and 250 ppb PCB (Aroclor 1248) twice weekly for a period of 1 year. Prior to being placed on the experimental diets, the general health status of the animals will be evaluated through extensive clinical chemistry evaluations including the levels of urinary and serum ketosteroid hormones at various stages of the menstrual cycle. After having been on the experimental diets for 6 months the monkeys will be bred to control male animals. The pregnant females will be evaluated throughout gestation for signs of impending difficulties. Abortions and stillbirths will be examined grossly and microscopically for abnormalities and levels of PCBs in the various tissues determined. The live infants born to those females will be examined for birth defects and skin and fat biopsies taken to determine level of transplacental movement of PCBs. The infants will be permitted to remain with their dams for 4 months. During this time monthly biopsies of the infant will be performed for PCB analysis. In addition, milk samples will be procured from the lactating females to determine the concentration of PCBs in the milk. After 4 months the infants will be placed on a milk replacer and continue to be evaluated clinically and behaviorally for abnormalities. Depending upon the response of the adult females to PCB exposure, they may be removed from the experimental diet when their infants are weaned and their rate of recovery from PCB intoxication evaluated. If there are no serious injurious effects of the exposure, we will continue the experimental diets for a second year. During this time we will continue to monitor their general body health and by biopsy procedures determine the rate of PCB accumulation in their adipose tissues. BIBLIOGRAPHIC REFERENCES: Allen, J.R., Carstens, L.A. and Abrahamson, L.J. Responses of rats exposed to polychlorinated biphenyls for fifty-two weeks. I. Comparison of tissue levels of PCB and biological changes. Arch. Environ. Contam. Toxicol. 4, in press (1976). Barsotti, D.A., Marlar, R.J. and Allen, J.R. Reproductive dysfunctions in rhesus monkeys exposed to low levels of polychlorinated biphenyls (Aroclor 1248). Food Cosmet. Toxicol. 14, in press (1976).